First Americans rushed into unknown from Asia

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A photo provided by André Strauss shows the excavation of a skeleton approximately 9,600 years old in a rock shelter in Brazil. New DNA analyses show the earliest known Americans split into distinct groups after they crossed a land bridge from Asia.
(André Strauss via The New York Times) - Bulletin

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A photo provided by André Strauss shows the excavation of a skeleton approximately 9,600 years old in a rock shelter in Brazil. New DNA analyses show the earliest known Americans split into distinct groups after they crossed a land bridge from Asia.
(André Strauss via The New York Times)8013580

Almost 11,000 years ago, a man died in what is Nevada. Wrapped in a rabbit-skin blanket and reed mats, he was buried in a place called Spirit Cave.

Scientists have recovered and analyzed his DNA, along with that of 70 other ancient people whose remains were discovered throughout the Americas. The findings lend astonishing detail to a story once lost to prehistory: how and when humans spread across the Western Hemisphere.

The earliest known arrivals from Asia were splitting into recognizably distinct groups, the research suggests. Some of these populations thrived, becoming the ancestors of indigenous peoples throughout the hemisphere.

But other groups died out, leaving no trace save for what can be discerned in ancient DNA. Indeed, the genetic research hints at many dramatic chapters in the peopling of the Americas that archaeology has yet to uncover.

“Now, this is the grist for archaeologists,” said Ben Potter of the University of Alaska, who was not involved in the new papers. “Holy cow, this is awesome.”

Earlier studies had indicated that people moved into the Americas at the end of the last ice age, traveling from Siberia to Alaska across a land bridge now under the Bering Sea. They spread southward, eventually reaching the tip of South America.

Until recently, geneticists could offer little insight into these vast migrations. Five years ago, just one ancient human genome had been recovered in the Western Hemisphere: that of a 4,000-year-old man discovered in Greenland.

The latest batch of analyses, published in three studies this week, marks a turnaround. In the past few years, researchers have recovered the genomes of 229 ancient people from teeth and bones discovered throughout the Americas.

One of them is a rare individual, only the second so-called Ancient Beringian whose DNA has been analyzed.

The first, described in January by Eske Willerslev, a geneticist at the University of Copenhagen, was a 11,500-year-old girl whose remains were found in eastern Alaska.

The second was discovered hundreds of miles away, in western Alaska, and lived 9,000 years ago, Willerslev and his colleagues reported Thursday in the journal Science.

The Ancient Beringians separated from the ancestors of living indigenous people in the Americas about 20,000 years ago. The findings suggest they endured for several thousand years. Then, they disappeared, leaving no known genetic trace in living people.

But another wave of migrants from Siberia did not stop in Alaska. They kept moving, eventually arriving south of the ice age glaciers. Then, they split into two branches.

One group turned and headed north, following the retreating glaciers into Canada and back to Alaska. The other branch took a remarkable journey south.

The genetic data suggest that this group spread swiftly across much of North America and South America about 14,000 years ago. The expansion may have taken only centuries.

“It’s basically an explosion,” Willerslev said.

The man from Spirit Cave in Nevada belonged to this southern branch of migrants. He was closely related to a 12,700-year-old boy found on the other side of the Rocky Mountains in Montana, Willerslev also found.

But the man from Spirit Cave turned out to have a close genetic link to 10,400-year-old skeletons found in Brazil, on the other side of the equator.

David Reich of Harvard University and his colleagues found a similar pattern in their research, published Thursday in the journal Cell.

They uncovered a link between the ancient Montana boy and another group of ancient South Americans, including a 10,900-year-old skeleton in Chile. Like Willerslev’s work, the kinship suggests that migrants moved quickly from North America to South America.

“We agree that this must be a rapid radiation,” Reich said.

Starting about 9,000 years ago, both teams found, additional waves of people moved southward. Willerslev’s research suggests the new arrivals mixed with older South American populations.

Reich, on the other hand, sees evidence for two waves of migrants who replaced the people who had lived in South America.

In 2015, Reich and his colleagues found that some living people in the Amazon carry DNA that’s most similar to that of people who live today in Australia and New Guinea.

The researchers speculated that their ancestry included an unknown group, which the scientists called Population Y, who separately made their way into the Americas.

In their study, Reich and his colleagues found no trace of Population Y — but Willerslev’s team succeeded in identifying their DNA in some of the 10,400-year-old skeletons in Brazil.

Perhaps another group of Asians entered the Americas long before the ancestors of the man from Spirit Cave and other early Native Americans. Maybe they interbred with people in the Amazon before disappearing.

Or perhaps a few of the early members of the southern branch happened to have some odd genes that survived through the generations.

The new rush of genetic samples reflects an improving working relationship between scientists and indigenous peoples. For decades, many tribes rejected requests for DNA from researchers.

The man from Spirit Cave, for example, was dug up by archaeologists in 1940 and stored in a museum. The local tribe, the Fallon Paiute-Shoshone, didn’t learn of the body till 1996. For years, they fought for its repatriation.

“It’s utterly disrespectful,” said Rochanne L. Downs, a member of the tribe’s cultural committee. “If someone went into Arlington Cemetery and dug up the grave of one of the soldiers and took their medals, there would be outrage.”

Initially, the tribe was opposed to looking for DNA in the skeleton, because scientists would have to destroy much of it. Willerslev met with the tribe and explained that he would require only a tooth and a small piece of ear bone.

The tribe agreed to give him one shot at finding DNA in the Spirit Cave remains.

Willerslev’s results led the Bureau of Land Management to turn over the skeleton to the tribe. They buried the man from Spirit Cave at an undisclosed location in 2017.

Downs wouldn’t rule out similar studies in the future, but said each request would require careful consideration.